The regasification facilities are used for regasification of LNG, i.e., to turn LNG back into natural gas. There facilities can be identified into two different types, onshore and offshore. In onshore facilities, LNG storage and regasification units are installed onshore, whereas offshore facilities include a floating LNG storage unit, usually an LNG carrier or a gravity based structure (GBS), and a regasification unit installed on the floating structure, a shuttle regasification vessel (SRV) or a LNG regasification vessel (RV).
The SRV or the LNG RV is special purposed vessels that can navigate with regasification facilities. The procedure starts by loading LNG from where it is produced and transports to an unloading location where then it is moored by submerged turret loading (STL) in offshore. These vessels have been widely used in the US, etc. for supplying natural gas and have been constructed by several Korean shipbuilding companies.
In light of growing of LNG demand, many attempts have been considered to construct new FSRU, but only several second-handed LNG carriers had been converted to FRSU due to economical reason and time constrains to deliver in Latin America and Asia, etc.
Construction of onshore facilities, however, faces more severe constrains. A large site has to be secured near facilities where LNG carriers are moored, and large scale construction incurs high cost, complex civil appeals of neighboring residents, and immobility of the facility once the construction is over. Thus, in many cases, offshore facilities are considered as a better solution for the fast tract of supplying natural gas.
Nevertheless, when newbuilding or conversion of FRSU is considered, the construction period expands to several years along with high capital costs. Also, when a second-handed LNG carrier conversion is considered, one has to account for the age of the vessel and cargo containment type, since it determines the conversion cost and period. With respect to the cargo containment type, LNG carriers with membrane cargo containment system have to go through a partial reinforcement on its membrane structure to support the regasification facilities on the upper deck. Storage of LNG and operation of regasification facilities are restricted due to the risk of sloshing damage from frequent partial loading of LNG.
Meanwhile, FSRU or SRV is moored to a jetty structure to withstand offshore weather and conditions. LNG is supplied to FSRU from LNC carrier (LNGC) through a loading arm installed on a jetty where both FSRU and LNGC are moored side by side. Once regasified by FSRU or SRV, high pressured natural gas (usually between 40 and 90 atm) is supplied to onshore through high pressure gas arm. During this process, because floating facilities like FSRU or LNG RV are influenced by tidal currents and wind, directional and rotational motions are accompanied. Thus, the loading arm and the high pressure gas arm have a large number of components which can absorb impact from the motions. If the FSRU or the LNG carrier is disconnected from the jetty beyond an operational range, the pipe line will automatically disconnect from the jetty for the safety. Although general LNG carriers are designed to operate under several pressures while loading and unloading of LNG, FSRU and LNG RV are constantly exposed to high pressure natural gas leak which can cause a fire or an explosion.